Influence of environmental pH on the reactivity of Candida albicans with salivary IgA

Salivary secretory IgA reacts with a group of heat-shock mannoproteins pref erentially expressed on Candida albicans yeast cells and germ tubes grown a t 37 degrees C. Since other environmental factors can also modulate the exp ression of those antigens, we have investigated the influence of the pH of the culture medium on the expression of the antigens reacting with human sa livary IgA by C. albicans. By indirect immunofluorescence, yeast cells grow n in Sabouraud glucose broth at 37 degrees C showed a statistically signifi cant increase in reactivity with salivary IgA (p < 0.0001) when compared wi th cells grown at 25 degrees C at the 4 pH values studied (3.3, 5.9, 7.5, a nd 9.5), the highest reactivity and the major heat-shock effect being obser ved at pH 5.9. The decrease in reactivity with salivary IgA observed in C. albicans cells grown at pH values of 3.3 and 9.5 was confirmed by Western b lotting. Salivary IgA reacted with polydispersed materials from the cell wa lls of molecular masses > 55 kDa, which were more expressed at neutral pH t han at acidic or alkaline pH values. A. similar reactivity was observed whe n the antigenic extracts were stained with an antiserum directed against ol igosaccharides present in antigen 6 of C. albicans serotype A. The differen ces in reactivity presented by salivary IgA may be related to a decrease in the expression of polysaccharides present on the surfaces of the yeast cel ls of C. albicans grown at acidic or alkaline pH values. The low reactivity of salivary IgA with C. albicans cells grown at acidic pH values may help to explain the association between acidic saliva and the carriage of Candid a in the oral cavity, as well as with oral candidiasis.